A problem with conventional driver circuits is that the time delays between the input connection of the driver circuit and the output connection are relatively long, i.e. the reaction times upon interferences are relatively high. Furthermore, the minimum "on" inhibit times cannot be adjusted to a short enough value and there is a definite limit to the clock frequency duty cycle ranges.
From DE 36 14 832 C2 it has been known to provide a galvanically separating signal transmission circuit which generates galvanically separated output signals from digital input signals through an input coil and a switch-operated output coil spaced apart from the input coil. The coils are spaced such that practical reaction force nondirectional output signals are provided at the terminals of the output coil. A purpose of this circuit is to provide for a sufficient voltage strength which is subject, at the same time to only a small number of switching operations.
From DE 29 12 693 A1 it has been known to provide a buffer amplifier using a transformer for the potential separation of pulses. The buffer amplifier is designed such that it operates very accurately in that supply currents and signal currents are separated.
DE 21 03 091 A1 describes a transistor chopper modulator comprising a transformer in which a grounded shield is mounted between the primary and secondary windings wound adjacent to each other on the transformer core for the purpose of minimizing interferences. With said modulator it is to be ensured that no spurious signals occur.
DE 25 25 741 B2 shows a clock pulse system comprising a rather complex transformer in which the primary and secondary windings are wound on the core of the transformer as two intertwined wires. With the described arrangement two symmetrical timed pulse signals can be generated and distributed free of a DC portion.
From Patents Abstracts of Japan, Sect. E, vol. 2 (1978) No. 145 (E-75) referring to JP 53-112048 A2 it has been known to provide a signal isolating circuit supplying an analog output signal free of interferences from a transformer having at least one or more windings and a sample holding circuit with a saturated core.
Patents Abstracts of Japan, Sect. E, vol. 6 (1982), No. 205 (E-136) referring to JP 57-113606 A describes an isolation amplifying circuit which is used as a control means for signal transfer. The sample period and the phase are adjusted such that the excitation current equals zero. This allows the use of a transformer and a simple circuit providing high accuracy at the same time.
An insulating type voltage detector has been known from Patents Abstracts of Japan, Sect. E, vol. 12 (1988), No. 124 (E-601) referring to JP 62-25 07 04 A, which serves to reduce the number of parts and improve at the same time the reliability of the circuit in that the output signal of an inverter is used directly as an activation signal for an insulating amplifier.
The present invention is therefore based on the problem of providing a driver circuit which allows short signal propagation delays, is compact, has a broad signal clock frequency band width and has increased operational safety.